1. Field of the Invention
The present invention relates to a device for determining the signal term to be transmitted to a railroad traction vehicle from the respective, admissible top speeds for the travel path elements lying in the route covered by a signal light or by a, preferably, punctiform train influencing device.
2. Description of the Prior Art
In earlier signaling systems, in which the so-called push-button signaling technique was employed, the signal term to be connected to a signal light was derived from the combination of the respective end destination key actuated for the route position. A specific signal term is allocated to each possible key combination. This method of signal term selection has disadvantages, particularly when an overall route is composed of a plurality of partial routes, as is the case, for example, given train routes over a plurality of signaling zones. Therefore, in more recent track plan push-button signaling technology, one proceeds from the consideration that a signal term to be transmitted to a traction vehicle, apart from special cases, is determined by the switches in the travel path and the length of the braking distance coming into question. The admissible top speed can be selected for each position of every switch and for every braking distance. The velocity values prescribed for the individual route elements of a train path to be set are to be evaluated for determining the signal term to be transmitted to an approaching train according to the rule: the lowest velocity message determines the signal term. In order to derive the lowest velocity message, after a travel route has been determined, the route elements participating in the travel route are induced to emit the velocity message allocated thereto. The various velocity messages are received, examined and evaluated by a central receiving device, the so-called signal selection group. The result of this evaluation, the respectively lowest velocity message, is then forwarded via a closed circuit network to the appertaining signal group of the route start element, which is prepared to receive. The transmission of the signal term determined in such a manner to the approaching train occurs optically by signal light and/or electrically by train influencing elements, which preferably operate on a punctiform basis.
The described operation of signal selection is brief. The central receiving device is occupied for a maximum of 0.5 seconds. Despite this relatively short seizure time, an undesired waiting dependency of a plurality of routes pending for a signal selection can occur, since a random number of routes can simultaneously acquire their velocity term, but the central signal selection group is present only once and is exploited on a time division multiplex basis.
Given a failure of the central signal selection group, the entire signaling system is affected, because none of the signal light or, respectively, the train influencing devices operating in a punctiform manner can be controlled.